Piling Systems: Screw Piling

SCREW PILING

We have been in the screw piling business for over twenty years and have pioneered their use in all types of projects across the country; from cyclone shelters in Cape York Peninsula to the Olympic Beach Volleyball Grandstand at Bondi Beach. Screw piling is an integral part of our product and service offering because of its diversity, sustainability, strength and longevity; representing approximately 65% of our entire business. With five construction arms and three manufacturing plants across the country, we have grown to become industry leaders in today’s increasingly competitive market, with a reputation for high-quality and cost-effective solutions.

 

Technically Excellent

 

Managing loads of up to 100 tonne or 1000kN our screw piles are designed, manufactured and installed to effectively transfer building loads via the shaft to the helix located at the bottom of the shaft. With high bearing and tension capacity that exceeds requirements, they are suitable for a wide range of installations; including sails, signs and wind-prone buildings. Our unique screw pile system can reach depths of 48 metres and with low head-room clearance they are ideal for underpinning internal and under building jobs.

 

Environmentally-Friendly and Cost-Effective

 

Installed many times faster than driven piles and suitable for all soil types, screw piles offer a cost effective and time saving solution to meet your project requirements. Vibration free and environmentally friendly, they gain further efficiency savings by making low noise and producing no spoil. Our expert team is also certified to conduct both static load and lateral load testing, ensuring that SFL Piletech can offer an end-to-end solution for all your screw piling needs.

What Are Screw Piles?

Screw piles are ideally a form of deep foundation with a helix near the piles, so that the piles can be screwed securely into the ground. This process is quite similar to screwing onto wood, though the screw piles are screwed into the ground. Depending on the usage and ground conditions, they may have one helix (a screw) or more.

Screw piles offer an efficient means of installation, since they can be installed quickly, with limited vibration and noise. Moreover, their mechanism of load dispersion coupled with their efficient installation makes them ideal in a wide range of soils, including the earthquake prone zones that have a liquefaction potential.

How Screw Piles Work

Piles are usually made up of a hollow steel section, along with one or more helices attached to it. When being screwed into the ground, screw piles essentially cut into the soil in a constant pitch, rather than just auguring through it. The helical shafts and flights are usually made in such a way that they suit specific ground conditions.

When the piles reach the intended depth, they remain permanently secured in place, and the gaps are typically filled with concrete. The part left protruding on the ground provides an incredibly powerful reinforcement, where the building structure can be connected, or in some cases increase the capacity of the piles.

How are Screw Piles Installed?

In comparison to a standard concrete foundation, installing screw piles takes significantly less time, and utilizes less machinery and therefore less costs. Depending on the size of the pile, a wide range of plant sizes can be used for the installation, including hand held machines. In most cases, only one machine will be required when installing a steel screw pile foundation. Screwed piling is typically installed using a hydraulic torque drive.

In order to screw a screw pile securely into the ground, powerful hydraulic motors are used, since they have the capacity to apply the large torques required for the installation. Typically, these motors are fastened into the handling machines, which usually come in wide range of sizes, from 0.5T Bobcats and 20T Excavators, up to 100T crane rigs (mast mounted). The necessary handling machines and hydraulic motors required for the operation are usually determined by:

  • Torsional capacity of shafts
  • Positional tolerances
  • Minimum torque requirements for the installation
  • Site ground and soil profile conditions
  • Site access limitations in terms of width and height
How Screw Pilings Are Connected

One of the most important part of the design when it comes to piles is the interface between the pile and the building, and it therefore requires utmost care. The connection is ideally designed and constructed while considering the building and the soil/ground conditions where the piles are to be screwed. This process will require a geo-technical analysis, as well as a structural input from a professional.

Casting the head of the screw pile into the concrete foundation of the building is the most common way of connecting a screw pile into the foundation of a structure. Rigidity is achieved by casting steel reinforcement bars into the piles, and protruding them out into the building’s footing. The reinforcing bars are generally bent at 90 degrees, and this can sometimes be substituted with Reidbar reinforcement with footplates or flange nuts screwed into the ends.

How Durable are Screw Piles?

Well, all steel corrodes at some point. But most designs have this into consideration, and you can be sure that quality piles can perform as they should for their entire lifetime. To address corrosion, consider the following:

  • Surface protection should be applied onto the steel in order to limit the rate of corrosion
  • Remember to allow for some sacrificial corrosion, which is the predetermined rate of corrosion in line with the accepted standards
Why Use Screw Piles?

1. Fast installation

The installation of screw piles is ideally a one-step process where pre-fabricated screw piles are screwed into the ground. The rate is typically about 180m a day. Keep in mind that this is not affected by the presence of ground water, and therefore dewatering is not necessary.

2. Not necessary to Remove Soil

Since screw piles naturally displace soil as their shaft penetrates into the ground, you don’t have to pay for the soil to be removed from the site. This can be incredibly beneficial especially when the ground you are working with is contaminated.

3. Minimal ground disturbance and vibration

With screw piles, there’s no hammering or thumping because they use the screw action to penetrate the ground.

4. Accessibility to Restricted Areas

One of the major advantage with screw piles is that they can be installed on sites with little width or headroom, where machines used for driven or bored poles simply can go. The more versatile and smaller equipment ensure that the screw piles can be successfully installed around other plants or structures, which essentially makes retrofitting of piles feasible.

5. Incredible Earthquake Performance

In general, screw piles have a high ductile response and tensile strength. This is a major benefit in earthquake prone zones, as piles can resist the lateral displacement and tensile forces caused by an earthquake. Since they are predominantly and end-bearing pile, the effects of negative skin friction won’t be as severe as other piling systems would.

The helix does an excellent job of carrying the tension loads, so that when the soil liquefies, there will be minimum reduction in terms of capacity from the lost action of the shaft. The helix should be embedded in a sufficient depth, to reach the non-liquefiable layers so that it can handle the tension loads in case of a seismic event.

Uses of Screw Piles

While screw piles were originally developed for use in the nautical industry, they have now found their way in civil engineering, road, rail, and telecommunications. Their ability to bear large compression and tensile loads makes them ideal for signs, masts, and other retaining structures. They can also be used in homes projects such as in deck and fence construction.

SFL Piletech specialises in structural screw piles and is one of the industry leaders in the market today. SFL Piletech offers a diverse range of screw piles for loads up to 100 tonne or 1000 kN SWL. In some cases loads can exceed this base limit and SFL Piletech has a team of engineers able to calculate specially designed screw piles for almost all load cases, and situations.

There are many benefits of screw piles over other systems including;

  •  Up to 20 times faster installation then driven piles,
  • Vibration-less,
  • No dewatering requirements,
  • Re usable, recyclable,
  • Suitable for all soil types,
  • Installed using calibrated torque correlation to soil type and strength.
  • No reinforcement requirements
  • Simple connection to footings and structures above
  • Can be used as out of ground sub floor supports
  • Immediate load restraint
  • Eco sensitive, minimal impact
  • Nil onsite spoil

Screw piles transfer building loads via the shaft (typically CHS section, 76mm OD-406mmOD) to the helix located at the bottom of the shaft. Sizes and thicknesses of each member is engineer designed to allow for all design loads and geotechnical conditions.

SFL Piletech also offers specialised testing equipment for screw piles (static load testing, and lateral load testing), SFL Piletech manufactures all screw pile and components in its large 2500sqm factory located in Yatala, south Brisbane QLD. This manufacturing facility is capable of supplying large volume screw piles at short notice, all whilst under the supervision of design engineers.

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